Dye forming reactions are used in the oxidase test for detection of oxidase-positive organisms.
The oxidase test is based on the bacterial production of an intracellular oxidase enzyme. See Biochemical Tests for Identification of Medical Bacteria, p. 250, J. MacFaddin, Williams and Wilkins Co. Oxidase-positive organisms include Pseudomonadaceae, Moraxella, Nesseria, Aeromonas, Vibrionaceae and Pleisiomonas shigelloides.
Oxidase-positive organisms produce reduced cytochrome c oxidase. It is oxidized in the presence of oxygen. Oxidized cytochrome c oxidase oxidizes primary amines such as dimethyl-p-phenylenediamine which in turn reacts with .alpha.-napththol to form indophenol blue. The formation of indophenol blue signals the presence of an oxidase-positive organism.
The reaction of oxidized dimethyl-p-phenylenediamine and .alpha.-napththol, however, provides a relatively insensitive test and the resulting dye is unstable, thus failing to indicate the presence of oxidase-positive organism in some cases.